Mike
A couple of comments:
1) You said below
Optional here means "not required by the DFDL
format", as in occursCountKind cannot be 'parsed' at all, because
all occurrences are then not required, and the min/maxOccurs are only examined
for validation purposes, also occursCountKind cannot be 'implicit' for
the same reasons, and occursCountKind 'expression' also.
OccursCountKind 'implicit' is allowed, because
minOccurs is used for parsing and micOccurs can not be 0.
2) You said below
Wrapping the array element in a sequence doesn't solve
the problem unless the sequence has a required piece of syntax such as
an initiator or terminator, or a hiddenGroupRef to a not-optional (recursively)
thing.
A sequence has minOccurs '1' so it does satisfy
the spec rule about the child of a choice being required. Such a sequence
could have no syntax and could contain an element with minOccurs '0' or
even be empty. I have seen DFDL schemas that contain a choice with the
last branch being an empty sequence that contains an assert fn:false()
in order to throw a processing error.
Regards
Steve Hanson
Architect, IBM
DFDL
Co-Chair, OGF
DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
From:
Mike Beckerle <mbeckerle.dfdl@gmail.com>
To:
Alex Wood1/UK/IBM@IBMGB
Cc:
"dfdl-wg@ogf.org"
<dfdl-wg@ogf.org>
Date:
27/04/2015 13:35
Subject:
Re: [DFDL-WG]
OCK expression and count of 0 for a choice member....
Sent by:
dfdl-wg-bounces@ogf.org
I believe any use of occursCountKind 'expression' on an
element that is the first element on a branch of a choice should be an
SDE.
This is one of the cases where DFDL requires one to introduce
an element that would not be necessary in an ordinary XML schema, but is
necessary because DFDL does not have XML's easily parsed syntax to depend
on.
This is my opinion. I think we need to look at whether
this restriction is either
(a) necessary
(b) necessary to avoid excessive complexity in implementations
(c) unnecessary - but is the intention of what is specified
already (despite shortcomings of the prose/description in the spec, which
could be corrected.)
(d) an error in the specification
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology
| www.tresys.com
Please note: Contributions to the DFDL Workgroup's email
discussions are subject to the OGF
Intellectual Property Policy
On Mon, Apr 27, 2015 at 5:49 AM, Alex Wood1 <WOODA@uk.ibm.com>
wrote:
Hi Mike,
Can you clarify if you are saying that OCK expression should be prohibited
completely on a choice member (as occurrences for OCK expression are potentially
optional regardless of minOccurs value)
Or is your statement that it should cause an SDE specific to the count==0
case?
Kind Regards,
- Alex
Alex Wood -
Software Engineer -
WebSphere Message Broker Development
DFDL Development
MP 211, IBM UK Labs, Hursley Park, Winchester, Hants. SO21 2JN.
Tel: Internal 246272, External 01962 816272
Notes: Alex Wood1/UK/IBM@IBMGB
e-mail: wooda@uk.ibm.com
From: Mike
Beckerle <mbeckerle.dfdl@gmail.com>
To: Alex
Wood1/UK/IBM@IBMGB
Date: 24/04/2015
15:10
Subject: Re:
[DFDL-WG] OCK expression and count of 0 for a choice member....
I think this is an SDE.
Choice branches cannot be optional.
Optional here, does not mean minOccurs == 0, because for many occursCountKinds,
that's never checked unless validation is on, and validation doesn't guide
parsing anyway.
Optional here means "not required by the DFDL format", as in
occursCountKind cannot be 'parsed' at all, because all occurrences are
then not required, and the min/maxOccurs are only examined for validation
purposes, also occursCountKind cannot be 'implicit' for the same reasons,
and occursCountKind 'expression' also.
Wrapping the array element in a sequence doesn't solve the problem unless
the sequence has a required piece of syntax such as an initiator or terminator,
or a hiddenGroupRef to a not-optional (recursively) thing.
Even initiator and terminator are tricky, because in a non-delimited format,
those can be %WSP*; which can match nothing at all; hence, they do not
"require" any syntax.
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com
Please note: Contributions to the DFDL Workgroup's email discussions are
subject to the OGF
Intellectual Property Policy
On Fri, Apr 24, 2015 at 9:07 AM, Alex Wood1 <WOODA@uk.ibm.com>
wrote:
Hi All,
Please see below for a history of the issue.
This arose from fuzz testing of the IBM DFDL parser which produced a test
with a coutn of 0 for an OCK expression array which was a choice
member. And subsequent reference to the specification.
It was not clear what the correct outcome should be in a choice where the
first member is an array using OCK expression where the count resolves
to 0.
a.) resolve the choice to the zero length array
b.) move to the next choice branch
c.) throw an error
Kind Regards,
- Alex
Alex Wood -
Software Engineer -
WebSphere Message Broker Development
DFDL Development
MP 211, IBM UK Labs, Hursley Park, Winchester, Hants. SO21 2JN.
Tel: Internal 246272, External 01962 816272
Notes: Alex Wood1/UK/IBM@IBMGB
e-mail: wooda@uk.ibm.com
From: Steve
Hanson/UK/IBM
To: Alex
Wood1/UK/IBM@IBMGB
Cc: Andrew
Edwards/UK/IBM@IBMGB, Mark Frost/UK/IBM
Date: 24/04/2015
09:19
Subject: Re:
OCK expression and count of 0 for a choice member....
When I wrote the paragraph below, the one thing that troubled me was that
the spec defines known-to-exist and known-not-to-exist in terms of occurrences.
In the choice branch example, it is the element as a whole we are looking
at. That's fine for scalar as element == occurrence but for an array it's
not the same. I think the spec is missing a definition of what 'missing'
means for an array element. I would say that an array element is missing
if all occurrences are missing. And an array element is not missing if
any occurrence has a representation (empty, nil, normal). With that
in place, my paragraph makes sense, I think.
I believe we have the same issue with 'parsed' and 'stopValue'.
Regards
Steve Hanson
Architect, IBM
DFDL
Co-Chair, OGF
DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
From: Steve
Hanson/UK/IBM
To: Alex
Wood1/UK/IBM@IBMGB
Cc: Andrew
Edwards/UK/IBM@IBMGB, Mark Frost/UK/IBM@IBMGB
Date: 23/04/2015
18:52
Subject: Re:
OCK expression and count of 0 for a choice member....
Here is one interpretation...
A choice is resolved by parsing the branches until one is known-to-exist
as described in section 9.3.3. Section 9.3.1.2 defines known-to-exist
(in the absence of a discriminator, initiator or direct dispatch) as an
occurrence having empty, nil or normal representation. Section 9.3.1.3
defines known-not-to-exist (again in the absence of a discriminator, initiator
or direct dispatchm or an assert) as an occurrence being missing or causing
a processing error. If occursCount is zero no occurrences are looked for
in the data (erratum 5.9) so the element has no representation and must
be missing. Therefore a choice branch containing such an element is known-not-to-exist.
So in your example, the first choice branch containing myInt is known-not-to-exist
and the parser tries the next branch.
This appears to contradict section 15.1.1 though. I suspect that 15.1.1
was not updated to match section 9.3 when the latter was added.
If you want to make the first choice branch known-to-exist when the count
is zero then I think wrapping myInt in a sequence would work. Or wrapping
myInt in a complex element.
Definitely one to take to the WG though, if only to correct section 15.1.1
to match section 9.
Regards
Steve Hanson
Architect, IBM
DFDL
Co-Chair, OGF
DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
From: Alex
Wood1/UK/IBM
To: Steve
Hanson/UK/IBM@IBMGB
Cc: Andrew
Edwards/UK/IBM@IBMGB, Mark Frost/UK/IBM@IBMGB
Date: 23/04/2015
16:33
Subject: OCK
expression and count of 0 for a choice member....
Hi Steve
Just been discussing this with Andy and Mark.
I think the spec
<xs:element name="Choice_Expression" dfdl:ref="config"
dfdl:lengthKind="implicit">
<xs:complexType>
<xs:sequence dfdl:ref="config">
<xs:element ref="myCount"></xs:element>
<xs:choice
dfdl:choiceLengthKind="implicit" dfdl:ref="config">
<xs:element
ref="myInt" minOccurs="1" maxOccurs="3"></xs:element>
<xs:element ref="myTxt"></xs:element>
</xs:choice>
</xs:sequence>
</xs:complexType>
</xs:element>
Where myInt
has occursCountKind="expression"
occursCount="{../myCount}"
A given instance of this message could have myCount==0
Is this valid?
Should it resolve to 0 occurrences of myInt or move on to myTxt ?
Section15 of the spec says:
The Root of the Branch MUST NOT be optional. That is XSDL minOccurs MUST
BE greater than 0.
But in this case minOccurs is >0.
Assuming this is not an error then in terms of resolving the choice section
15.1.1 says..
15.1.1 Resolving Choices via Speculation Speculative resolution works as
follows:
1) Attempt to parse the first branch of the choice.
2) If this fails with a processing error
a) If a dfdl:discriminator evaluated to true earlier on this branch then
the parser is 'bound' to this branch and parsing of the entire choice construct
fails with a processing error.
b) If the branch has a dfdl:initiator and the choice has dfdl:initiatedContent
‘yes’ then the parser is 'bound' to this branch and parsing of the entire
choice construct fails with a processing error. c) Otherwise we repeat
from step 1 for the next branch of the choice.
3) It is a processing error if the branches of the choice are exhausted.
4) If a branch is successfully parsed without error, then that branch's
infoset becomes the infoset for the parse of the choice construct.
So seems like this is 4.) we did not fail to parse myInt...
However talking with mark about real scenarios that this might apply to,
a choice two repeating fields with counts earlier in the data only one
of which must appear. you'd expect 0 of the first means >0 of the second
and visa versa... So you'd probably want 0 myInt allowed the choice to
resolve to myTxt.
Thoughts ?
If you agree we need more clarity in he spec will forward to WG.
Kind Regards,
- Alex
Alex Wood -
Software Engineer -
WebSphere Message Broker Development
DFDL Development
MP 211, IBM UK Labs, Hursley Park, Winchester, Hants. SO21 2JN.
Tel: Internal 246272, External 01962 816272
Notes: Alex Wood1/UK/IBM@IBMGB
e-mail: wooda@uk.ibm.com
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741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
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741598.
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dfdl-wg mailing list
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Unless stated otherwise above:
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741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU